1. Both Meg and Amy used to be afraid of the dark. (Meg used to be afraid of dark. So did Amy.)
2. Phil wants to be either a doctor or a dentist. (Phil wants to be a doctor. He wants to be a dentist too.)
3. Both Mark and Rob aren't afraid of heights. (Mark isn't afraid of heights. So isn't Rob.)
4. Both my mum and my grandma hate crowds. (My mum hates crowds. So does my grandma.)